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1. Abstract
During 1970, the first two supersonic aircrafts entered service, created aviation excitement. These supersonic aircrafts were Concorde and TU 144. The Concorde started operating in 1977 and the TU 144 in 1978. Both aircraft promised to completely revolutionize commercial transportation, providing speeds over twice the speed of sound (around 1100 mph vs. 500-600 mph for other commercial airliners). Most thought the supersonic transport would replace other aircraft, to become the norm in general aviation. However, a successful supersonic aircraft design has to overcome numerous challenges to meet opposing requirements. In this text the history of supersonic aircraft, past failures, their functional requirements, design challenges, advantages, disadvantages and mitigation techniques are presented.
2. Introduction
Supersonic aircraft are the aircraft that travels with the speed more than mach 1. Mach 1 is the speed of sound. The aircraft travelling with the speed very large than the speed of sound is known as hypersonic aircraft (above mach 5). In the current global economy, where individual companies as well as business partnerships, transcend national boundaries, and mandate collaborations across the globe, the required time for travel has become a valuable resource, prompting interest in high speed transportation. Compared to today’s typical transport aircraft mission profiles with cruise flight speeds of Mach M=0.8 and design ranges of 4000 nautical miles (nm), up to a 55% time savings can be achieved by increasing the cruise speed to M=1.8 [1]. However, a successful supersonic aircraft design has to overcome numerous challenges to meet opposing requirements.
3. History:
60 years ago Chuck Yeager, captain of United States air force, broke the sound barrier while flying his bell X-1 aircraft. That was the beginning of the supersonic flight era. Since then, numerous advances have been made, from the introduction and design improvements of military supersonic jets to the innovation aimed at passenger supersonic flight. Concorde was the first supersonic aircraft used for passenger travel
4. Functional requirements:
1. The aerodynamics of supersonic flight are dramatically different from those of subsonic flight (i.e., flight at speeds slower than that of sound). In particular, aerodynamic drag rises sharply as the aircraft passes the transonic regime, requiring much greater engine power and more streamlined airframes.
2. To keep drag low, wing span must be limited, which also reduces the aerodynamic efficiency when flying slowly. Since a supersonic aircraft must take off and land at a relatively slow speed, its aerodynamic design must be a compromise between the requirements for both ends of the speed range.
3. The structural sizing needs to balance minimum weight with adequate safety margin to support high loads at high speed.
4. Engine must be compact and should consume less fuel.
5. The need for efficient fuels is tied to the need to reduce the fuel contribution to the weight of the aircraft, both in terms of fuel weight and the weight of the rest of the aircraft using this fuel for propulsion, because the weight is a major contributor to the sonic boom and the drag. The fuel and propulsion system also affects the emission levels of NOx at high altitudes as well as the cruise efficiency, leading to changes in aircraft configuration[2].
6. Environmental constraints are becoming more and more stringent. The high altitude emission should be as low as possible. Again the sound produce by supersonic aircraft while taking and landing should be within the limit, so that it is not harmful to human beings. The sound produce by sonic boom should also be less[3].
7. The heat generated by friction as the air flows over the aircraft is very high therefore the material should have the capacity to withstand the high temperature.
8. The ticket price should be low.
5. Advantages of supersonic aircraft:
1. The value of time has been growing, resulting in a premium being placed on the ability to get to the destination faster.
a. Supersonic aircraft reduces travel time for business leading to increased productivity. It also shortens travel time for leisure.
b. It has the ability to provide rapid response in disaster situations and faster delivery of time-critical goods[2].
2. Supersonic aircraft quickly delivers the time-critical cargo which could save lives, as in the case of organ transplants[2].
3. It is also useful for defence in military.
a. Supersonic speed with manoeuvrability provides amazing dog fighting ability to fighter aircraft.
b. Supersonic aircraft can quickly and safely attack enemy targets.
c. Supersonic speed allows fighter jets to intercept enemy airplanes. Supersonic interceptors can quickly reach their target if the target is slow, in a matter of minutes if they are close by. (The hijacked airplanes of 9/11 should have been intercepted.)
6. Disadvantages:
1. Sonic boom:
A major problem, which all supersonic aircrafts face, is sonic boom. The term sonic boom is used to refer to the shocks caused by the supersonic flight of an aircraft. Sonic booms generate enormous amounts of sound energy, sounding much like an explosion[4]. Sonic boom is the reason why supersonic flights are not allowed over populated areas.
When aircraft travels at the speed less than sound, the sound it creates will propagate in all the directions ahead of the plane as shown in fig.2 when it travels with mach 1 the wave propagation is also shown in fig.2. Now when it travels with the speed greater than sound, it travels faster than the sound wave it creates and it breaks the sound barrier and it forms the cone like structure behind the aircraft as shown in fig.2. The visual impact of the sonic boom is shown in fig.3. It is because of the speed with which aircraft is travelling causing the pressure to drop significantly which in turn reduces the temperature causing condensation in the air.